Materials Science · Cross-listed from physics.comp-ph
Mixture of Experts Framework in Machine Learning Interatomic Potentials for Atomistic Simulations
Gabriel de Miranda Nascimento, Marc L. Descoteaux, Laura Zichi et al. (+9 more)
First-principles atomistic simulations are essential for understanding complex material phenomena but are fundamentally limited by their computational cost. While Machine Learning Interatomic Potentials (MLIPs) have drastically improved cost for a given accuracy, their inference cost remains a bottleneck for massive systems or long timescales. To address this, we introduce a multifidelity "Mixture-of-Experts" framework based on the E(3)-equivariant Allegro architecture. Our method spatially partitions the simulation domain into a chemically complex region (e.g., reactive interfaces) and a simple region (e.g., bulk
lattice), assigning models of varying capacity to each. Among the challenges in such static domain decomposition, the mechanical mismatch between models at the interface is particularly critical, as it can generate artificial stress fields and instability. We address this challenge with a co-training strategy in which the loss function includes agreement constraints – penalties on per-atom energy and force discrepancies between models evaluated on shared bulk environments – forcing the independent models to learn a consistent physical description of the bulk material. We validate this approach on a realistic Pt+CO catalytic system, demonstrating that the co-trained models maintain exact energy conservation, align their bulk mechanical response (e.g., equation of state and bulk modulus), and achieve predictive accuracy comparable to a full high-fidelity simulation at more than twice the computational speed.
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All authors Gabriel de Miranda Nascimento, Marc L. Descoteaux, Laura Zichi, Chuin Wei Tan, William C. Witt, Nicola Molinari, Sriteja Mantha, Daniil Kitchaev, Mordechai Kornbluth, Karim Gadelrab, Charles Tuffile, Boris Kozinsky
Statistical Mechanics · Cross-listed from quant-ph
Eugenio Bianchi, Pietro Donà and Erick Muiño
We consider a many-body
Hilbert space with a fixed global charge and show that the typical
entanglement entropy of a subsystem, at the leading and subleading order in the thermodynamic limit, can be expressed in terms of a single quantity which represents the local thermal
entropy at fixed charge density. We find a general formula which applies both to abelian U(1)
symmetry and non-abelian SU(2)
symmetry, including the case of a local
Hilbert space which transforms under a general reducible representation of the
symmetry group. We illustrate the general formula with model systems and discuss the relevance of the results as a probe of
quantum chaos for physical
Hamiltonians.
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Statistical Mechanics
Topological transitions in spin-ice induced by geometrical constraints
R. A. Borzi, E. S. Loscar and S. A. Grigera
We study the nearest-neighbor
spin-ice model subjected to a
magnetic field applied along the global [111] and [110] directions, focusing on the role of sample geometry in stabilizing topological phase transitions. While no Kasteleyn transition is expected for this field orientations in the thermodynamic limit, we show that constraining the transverse dimensions of the system qualitatively changes the behavior. For samples elongated along the field direction with finite transverse area, the divergence-free constraint quantizes the number of string excitations that can span the system. As a result, the magnetization evolves through a cascade of discrete transitions corresponding to the successive entry of individual strings. Using Monte Carlo simulations, we demonstrate that each transition is marked by sharp magnetization steps and peaks in the specific heat and susceptibility, whose amplitudes scale linearly with the system length. We complement the numerical results with an analytical treatment based on the
entropy - energy balance on a system with reduced dimensionality, deriving the critical fields associated with each topological sector. In the isotropic limit these transitions merge into a smooth crossover, but for anisotropic samples they remain sharply resolved, illustrating an unconventional mechanism by which finite geometry stabilizes topological phase transitions in frustrated magnets.
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Materials Science
Implementation of the hybrid exchange-correlation functionals in the SIESTA code
Yann Pouillon, Bill Clintone Oyomo, James Sifuna et al. (+6 more)
We present an efficient and accurate implementation of hybrid exchange-correlation (XC) functionals in the SIESTA code, enabling large-scale simulations based on Hartree-Fock-type exact exchange combined with strictly localized numerical atomic orbitals (NAOs). Our approach exploits a fitted representation of the NAOs in terms of Gaussian-type orbitals (GTOs), which allows for the analytical evaluation of four-center electron repulsion integrals (ERIs) via the LIBINT library. This framework is seamlessly integrated with SIESTA's real-space grid and sparse-
matrix infrastructure, and is combined with multiple screening techniques to control the computational complexity. We also introduce a fully analytical formulation of hybrid-functional forces and a dynamic parallel distribution scheme that ensures excellent scalability. We validate our implementation through
benchmark calculations on a broad set of systems (including
semiconductors,
insulators, and two-dimensional materials) and demonstrate that the HSE06 functional significantly improves the prediction of band gaps compared to PBE, in close agreement with G0W0 and experimental data. We analyze in detail the trade-offs between accuracy and computational efficiency as a function of the number of Gaussians, basis set range, and integral screening thresholds. Our results confirm that hybrid functional calculations in SIESTA are now feasible for large extended systems, making accurate first-principles predictions of electronic and structural properties accessible at scale.
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All authors Yann Pouillon, Bill Clintone Oyomo, James Sifuna, María Camarasa-Gómez, Xinming Qin, Carlos Beltrán, Fernando Gómez-Ortiz, Honghui Shang, Javier Junquera
Materials Science
Hidden Crossover and Relaxor-Like Response from Emerging Polar Skyrmion Correlations in Ferroelectric Superlattices
Zhiyang Wang, Fei Yang and Long-Qing Chen
Polar skyrmions in ferroelectric superlattices are nanoscale topological polarization textures typically regarded as weakly coupled objects confined to individual layers, with a role secondary to that of the underlying
symmetry-breaking order parameter. Here using large-scale phase-field simulations of ferroelectric superlattices, we uncover a hidden thermal crossover deep inside the ferroelectric phase, where polar skyrmions evolve from an uncorrelated, layer-resolved state into an interlayer-correlated ensemble. This crossover occurs without additional
symmetry breaking or a new order parameter, but produces a pronounced broad peak in the dielectric susceptibility. The anomaly originates from the competition between correlation-enhanced response, associated with the growth of interlayer skyrmion correlations, and polarization-induced stiffness, which suppresses dielectric fluctuations at low temperature. Under AC driving, the peak shifts with frequency, resembling relaxor ferroelectrics despite the absence of quenched disorder or polar nanoregions. Our results establish a disorder-free route to relaxor-like dielectric response and identify topological defect correlations as an organizing principle for thermodynamic anomalies, providing a mechanism distinct from conventional critical behavior associated with
symmetry breaking and divergent order-parameter fluctuations.
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Statistical Mechanics
Diffusion with conserved marginal distributions and information theory in fracton hydrodynamics
Vaibhav Mohanty and Sunghan Ro
Diffusion with multipole-moment conservation gives rise to transport laws that generalize Fick's law and has attracted growing
attention following experimental advances in strongly tilted optical
lattices. It was recently shown that conserving complete multipole-moment groups leads to subdiffusive dynamics governed by a nonlinear
diffusion equation, raising the question of whether hydrodynamic equations would also be nonlinear when the conservation law is imposed only at the subsystem level. Here we show that subsystem
symmetries generically produce nonlinear hydrodynamic equations with shear-only transport, in which any localization present in the initial marginal distributions is preserved at long times by the conservation of those marginals. A linear regime emerges only as a limiting case for small fluctuations around a uniform background. We derive the deterministic and fluctuating parts of the hydrodynamic equations in arbitrary dimensions and obtain the corresponding maximum-
entropy equilibrium distributions under constrained marginals. We also show that marginal-conserving
diffusion provides a concrete hydrodynamic realization of partial multipole-moment conservation, and we offer an information-theoretic interpretation in which total correlation decays monotonically even when pairwise mutual information does not.
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Materials Science
Domain-induced control of latent heat in freestanding BaTiO$_3$ membranes
Tapas Bar, David Pesquera, Arnau Villalobos-Martin et al. (+11 more)
Thin ferroelectric BaTiO$_3$ films often exhibit continuous transitions instead of the first-order behavior of bulk
crystals, a discrepancy usually attributed to epitaxial strain or dimensionality. Using quasi-adiabatic nanocalorimetry on freestanding BaTiO$_3$ membranes-free of clamping and substrate heat sinking-we show that domain morphology, not thickness or boundary conditions, controls the transition order. Thick membranes with large, monodomain-like regions display clear latent heat, whereas thinner membranes with dense 180$^{\circ}$ domain patterns show a continuous transition despite undergoing the same tetragonal-cubic structural change confirmed by x-ray diffraction. Piezoresponse force microscopy links this behavior to domain-size
evolution, and a Ginzburg-Landau analysis demonstrates how reduced domain size lowers the free-energy barrier, rounding a nominally first-order instability. These results identify domain morphology as the key determinant of ferroelectric transition order in
oxide membranes and establish design guidelines for enhancing caloric effects through domain engineering.
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All authors Tapas Bar, David Pesquera, Arnau Villalobos-Martin, Cristian Rodriguez-Tinoco, Umair Saeed, Kumara Cordero-Edwards, Jessica Padilla, Jose Manuel Caicedo Roque, Jose Santiso, Pol Lloveras, Leo Boron, Igor Lukyanchuk, Gustau Catalan, Javier Rodriguez-Viejo
Soft Condensed Matter
Kinetics of segregation of topologically-modified ring polymers in cylindrical confinement
Harsh Doshi, Shreerang Pande, Sathish K. Sukumaran et al. (+1 more)
In Escherichia coli (E. coli), entropic repulsion between the two daughter DNA ring
polymers under cylindrical confinement is believed to be an important factor governing chromosomal segregation. The repulsion can be enhanced by topological modifications, i.e., by the introduction of internal loops at certain locations along the contour of the circular DNA. However, the effect of topological modifications on the rate of segregation of ring
polymers remains unclear. Therefore, we systematically varied the number and the contour length of loops introduced at selected locations by crosslinking monomers. The appropriate crosslinking was motivated by observations that extruded loops are located mainly near the origin of replication (ori-proximal) region of the E. coli chromosome. This resulted in the chains becoming intrinsically anisotropic. Using Langevin dynamics simulations of these topologically modified bead-spring
polymers, we calculated the time required for segregation under cylinder confinement. With certain caveats, we found that increasing the number of loops resulted in a decrease in the time of segregation. In line with past work, we propose that this is due to the increase in the entropic repulsion between the
polymers upon increasing the number of loops. In addition to the number of loops, the contour length of the loops and the mutual orientation of the (anisotropic) chains in the initial configurations played a role in determining the time of segregation.
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All authors Harsh Doshi, Shreerang Pande, Sathish K. Sukumaran, Apratim Chatterji
Materials Science · Cross-listed from physics.comp-ph
Accelerating finite-element-based projector augmented-wave DFT calculations with scalable GPU-centric computational methods
Kartick Ramakrishnan and Phani Motamarri
Accurate large-scale Kohn-Sham density functional theory (DFT) calculations are essential for modeling complex material systems, including interfaces, defects, nanoclusters, and twisted two-dimensional
heterostructures. Achieving chemical accuracy at scales of $10^4$-$10^5$ electrons with practical time-to-solution, however, remains challenging for existing DFT implementations. We present GPU-centric computational methods and algorithmic innovations within a finite-element (FE) discretized projector augmented-wave (PAW) formulation (PAW-FE) for accurate, efficient, and scalable electronic-structure calculations on modern exascale systems. The FE discretization, developed within a collinear
spin formalism, accommodates generic boundary conditions and employs multi-resolution quadrature for accurate evaluation of atom-centered PAW integrals on coarse grids. The resulting generalized Hermitian eigenproblem is solved using residual-based Chebyshev filtered subspace iteration (R-ChFSI). Exploiting R-ChFSI's tolerance to inexact
matrix-multivector products, we employ an approximate inverse PAW overlap
matrix, mixed-precision arithmetic (FP32/TF32), and low-precision nearest-neighbor communication (BF16) during filtered subspace construction, along with block-wise computation-communication overlap to reduce cost while preserving robustness. These strategies yield up to $8\times$ and $20\times$ CPU-GPU speedups on Intel and AMD GPU architectures, respectively. Compared to plane-wave PAW methods, PAW-FE achieves close to 8$\times$ reduction in time-to-solution for 10,000-electron systems on NVIDIA GPUs, with larger gains at scale, and around 6$\times$ over norm-conserving FE approaches. We demonstrate scalability to 130,000-electron systems, establishing PAW-FE as an exascale-ready method for chemically accurate first-principles simulations.
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Mesoscale and Nanoscale Physics
Magnetononlinear Hall effect from multigap topology in metal-organic frameworks
Chun Wang Chau, Wojciech J. Jankowski, Bo Peng et al. (+1 more)
We unveil that non-Abelian multigap band
topology characterized by nontrivial Euler class invariants induces observable magnetononlinear
Hall transport phenomena. We demonstrate these effects in a highly-tunable class of recently synthesized two-dimensional kagome N-heterocyclic carbene (NHC) metal-organic frameworks. We showcase the controllability of the nonlinear effect upon applying external voltage, changing temperature, and chemical substitutions that preserve the bulk
topology and associated edge states. Our findings therefore reveal an uncharted presence of Euler class
topology in metal-organic materials that can be experimentally deduced through measurable magnetotransport.
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All authors Chun Wang Chau, Wojciech J. Jankowski, Bo Peng, Robert-Jan Slager
Strongly Correlated Electrons
QERNEL: a Scalable Large Electron Model
Khachatur Nazaryan and Liang Fu
We introduce QERNEL, a foundational neural wavefunction that variationally solves families of parameterized many-electron
Hamiltonians and captures their ground states throughout parameter space within a single model. QERNEL combines FiLM-based parameter conditioning with scale-efficient architectural elements – mixture of experts and grouped-query
attention, substantially improving expressivity at low computational cost. We apply QERNEL to interacting electrons in
semiconductor moiré heterobilayers, training a single weight-shared model for systems of up to 150 electrons. By solving the many-electron Schrödinger equation conditioned on moiré potential depth, QERNEL captures both
quantum liquid and
crystal states and discovers the sharp phase transition between them, marked by abrupt changes in interaction energy and charge density. Our work establishes a foundation model for moiré
quantum materials and a scalable architecture toward a Large Electron Model for solids.
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Strongly Correlated Electrons · Cross-listed from hep-th
The Schrodinger Equation as a Gauge Theory
Dmitry S. Ageev and Vladimir A. Bykov
The conserved probability current of the Schrodinger field admits a dimension-dependent gauge representation that provides a convenient setting for comparing hydrodynamic, topological and infrared structures. We use this representation to develop a unified treatment of several deformations of the Madelung momentum. BF couplings incorporate electromagnetic interactions, Berry and
spin connections, projected non-abelian adiabatic data, and intrinsic phase holonomy within the same framework. In $(2+1)$ dimensions, the Chern-Simons deformation can be reduced to a nonlocal functional of the wavefunction. Its Coulomb-gauge form separates into a phase-sensitive
geometric contribution and a density-dependent dynamical contribution; we show explicitly how this separation changes under a general gauge transformation and recover the topological braiding phase in the well-separated adiabatic regime. For systems with a spatial boundary, we derive the equal-time
symplectic structure, the associated surface charges, and their boundary
algebra. Finally, after a nonlinear interaction produces the Bogoliubov acoustic branch, the radiative
memory can be expressed in the dual two-form variables. Its zero-average component is generated by a residual large gauge transformation, whereas the monopole component remains independent global data. This provides a gauge-theoretic description of the
memory/asymptotic-
symmetry sector of the acoustic infrared structure.
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Mesoscale and Nanoscale Physics
Quantum Hall Liquids Coupled to Dynamical Electromagnetism
T. H. Hansson, Qing-Dong Jiang, S. A. Kivelson et al. (+1 more)
We investigate the effect on a
Quantum Hall (QH)
liquid of its coupling to 3+1 dimensional dynamical electromagnetism, which renders the system gapless. We calculate both the
Hall and longitudinal resistances, $\rho_H$ and $\rho_L$, in the context of a minimal model of the electromagnetic environment, with a small three dimensional conductivity ${\tilde{\sigma}}$, that allows for a counter-flow current. In the thermodynamic limit, we show that $\rho_H$ is quantized, while $\rho_L$ approaches a non-zero limit, $\rho_L \sim \alpha\, R_K$, where $\alpha$ and $R_K=2\pi /e^2$ are the fine structure and the Klitzing constant. In contrast, the QH conductance, $\sigma_H$, is smaller than the expected quantized value by a correction $\sim \alpha^2/R_K$. The electromagnetic interaction also generates corrections of order $\alpha^2$ to the quasiparticle charges and statistics, in a way that is consistent with general arguments based on gauge invariance. In addition, we present an intuitive argument that relates the flux attachment associated with the composite
boson representation of the electron
liquid to the empirically observed %persistence of approximate quantization of $\rho_H$, even in circumstances in which $\rho_L$, and the deviation of $\sigma_H$ from its quantized value, are substantial.
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All authors T. H. Hansson, Qing-Dong Jiang, S. A. Kivelson, Thomas Klein Kvorning
Superconductivity
Exposing impostor Majorana zero modes through atomic-scale shot-noise
A. Maiti, G. D. Gu and F. Massee
A robust zero-bias conductance peak in putative $p$-wave
superconductors is often regarded as the primary signature of a Majorana zero mode. Yet similar features can also arise from trivial bound states. This ambiguity has limited the reliability of conventional spectroscopy as a diagnostic tool, raising a long-standing problem of how to detect such impostors. Here, we address this issue with an alternative approach, atomic-scale shot-noise spectroscopy, that goes beyond conductance measurements. Through a detailed investigation of multiple defect-bound zero-bias states in the widely studied
superconductor Fe(Se,Te), we observe that differential conductance can exhibit an apparently `robust' zero-bias peak. However, shot-noise measurements consistently reveal the fingerprint of the individual particle- and hole character hidden in the tunnelling conductance, unambiguously exposing the trivial nature of the zero-bias peak. Our results establish shot-noise spectroscopy as a decisive diagnostic for ruling out false Majorana signatures in atomic-scale experiments.
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Disordered Systems and Neural Networks · Cross-listed from quant-ph
Solvable Random Unitary Dynamics in a Disordered Tomonaga-Luttinger Liquid
Tian-Gang Zhou and Thierry Giamarchi
Disordered one-dimensional interacting systems have long been characterized via conventional correlation functions. A complementary
quantum-information perspective quantifies the randomness of the
unitary ensemble dynamics generated by a
quantum system through the frame potential, which serves as a practical diagnostic for
quantum algorithmic performance. However, no analytical treatment has yet been achieved for experimentally accessible interacting one-dimensional systems. In this Letter, we derive a closed-form expression for the frame potential of a Tomonaga-Luttinger
liquid with quenched Gaussian forward-scattering disorder. Exploiting the exactly quadratic structure of the disorder-averaged Keldysh action, we show that the frame potential decays as a power law at early times and saturates to a late-time plateau controlled by a single coupling parameter. Taking the random field XXZ
spin chain as a specific microscopic realization, we show that the strongest randomness is achieved near the Heisenberg
ferromagnetic point and can be exponentially enhanced through a multiple-quench protocol. We validate our results across the entire gapless phase, with direct implications for
algorithm design in analog
quantum simulation platforms.
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Strongly Correlated Electrons
Towards a microscopic model for an electronic quantum charge liquid
Jacob R. Taylor, Sankar Das Sarma and Seth Musser
We provide a route to constructing an electronic
quantum charge
liquid (QCL), a state made up of
fermions at fractional filling of a
lattice that does not break translation. Starting with spinless
fermions at filling $\nu=3/2$ we pair them to get
bosons at filling $\nu=3/4$ per unit
cell. The tetramer model, a generalization of the dimer model, on the square
lattice is evaluated as a candidate bosonic QCL at filling $\nu = 3/4$. It is shown that these models exhibit a local $\mathbb{Z}_4$
symmetry. Upon numerical study of a family of tetramer wavefunctions it is found that while one is gapless due to $\mathrm{U}(1)^3$
symmetry at least one other can be definitively shown to be gapped. The gapped nature of this state, along with its $\mathbb{Z}_4$
symmetry, leads us to propose that it is an example of the elusive bosonic QCL displaying the minimal $\mathbb{Z}_4$ topological order. We conclude by discussing possible extensions to other
lattice geometries, electronic QCLs, and to Rydberg atoms.
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Disordered Systems and Neural Networks · Cross-listed from quant-ph
Characterization of Thermalization Behaviour in a Generalized Aubry-André Model
S. Mal, D. K. Nandy and B. K. Sahoo
Although random
matrix theory provides a fundamental framework for characterizing
quantum chaos, encompassing both ergodic and localized phases, a comprehensive understanding of the universal features governing the critical transition remains elusive in many disordered and quasi-random systems. In this study, we explore the ergodic-to-many-body localization transition in the generalized Aubry-André model with interacting spinless
fermions. Using the concept of Frobenius norm of an adiabatic gauge potential, we construct a phase diagram that captures the sensitivity of the eigenspectrum to infinitesimal adiabatic gauge deformations. To examine the stability of the critical disordered strength with respect to system size, we perform an unbiased finite-size scaling analysis via cost-function minimization techniques. Additionally, by analyzing the adjacent gap ratio and spectral form factor, we determine the scaling behavior of the Thouless time as a function of the disorder strength.
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Materials Science
Structure Prediction and Bonding Analysis of B$_{18}$Ag$_2$ Clusters Featuring Double-Ring Motifs
Peter Ludwig Rodríguez-Kessler
The structural stability, electronic structure, and bonding characteristics of the silver-doped boron cluster B18Ag2 were investigated using density functional theory (DFT) combined with global optimization techniques. Basin-hopping searches identify a bent double-ring structure as the global minimum, consisting of two stacked B9 rings symmetrically stabilized by Ag atoms located above and below the boron framework. The UV-Vis absorption spectrum exhibits weak transitions in the near-infrared region and intense bands in the visible and near-ultraviolet regions, reflecting delocalized electronic excitations within the boron framework. Charge analysis indicates moderate electron redistribution from Ag atoms to the boron scaffold. Real-space bonding analyses based on the electron localization function (ELF), reduced density gradient (RDG), and molecular electrostatic potential (MEP) reveal that bonding is dominated by {$\sigma$}-delocalization over the boron skeleton, while Ag-B interactions are weak, non-directional, and primarily electrostatic. The continuous annular electron delocalization within the double-ring structure suggests an aromatic-like character. These findings establish B18Ag2 as a silver-stabilized boron double-ring cluster in which global electron delocalization governs structural stability, while Ag atoms act as axial stabilizing centers that modulate the electronic structure. This work provides new insight into the role of coinage-metal doping in stabilizing extended boron nanostructures.
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Superconductivity
Thermodynamic Evidence of Tetracritical Topology in the $H$-$T$ Phase Diagram of UTe$_2$ for $H \parallel b$
Michal Vališka, Tetiana Haidamak, Andrej Cabala et al. (+4 more)
We report ultrasound velocity measurements on an ultraclean UTe$_2$ single
crystal with $T_c>2$~K for $H \parallel b$, performed up to 18~T and down to 0.33~K. The measurements provide the missing bulk thermodynamic evidence for an additional high-field phase boundary near $\mu_0H\sim14$–15~T. A distinct, non-hysteretic anomaly in the longitudinal $C_{33}$ mode, together with a weaker response in $C_{44}$, no resolvable anomaly in $C_{55}$, and a coincident kink in transverse magnetostriction, reveals a
symmetry-selective coupling to
lattice strain. This mode selectivity places constraints on the
symmetry of the field-induced superconducting component. The phase line remains nearly field-constant near 14~T and meets three other phase boundaries at a tetracritical point near 13.5~T and 1.25~K. The results complete the local tetracritical
topology of the $H$–$T$ phase diagram and support field-induced multicomponent superconductivity in UTe$_2$.
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All authors Michal Vališka, Tetiana Haidamak, Andrej Cabala, Petr Proschek, Andreas Hauspurg, Sergei Zherlitsyn, Vladimír Sechovský
Disordered Systems and Neural Networks
Excluded volume and molecular field in the Lennard-Jones fluid: a modified first-order perturbation theory
A. Trokhymchuk, V. Hordiichuk, R. Melnyk et al. (+1 more)
The equation of state and, more generally, the thermodynamics of the Lennard-Jones fluid have long served as a
benchmark problem in the statistical theory of fluids. Among available theoretical approaches, first-order perturbation theory occupies a special position: only at this level does the correction to the Helmholtz free energy admit an exact statistical-mechanical expression. In this work, we present a systematic, simulation-based assessment of a non-classical first-order perturbation theory in which the reference system incorporates the entire short-range part of the interaction, while the perturbation is confined to the remaining long-range tail. We show that this range-based decomposition transforms the perturbation contribution into a small, smoothly varying, near-mean-field quantity over a broad supercritical thermodynamic domain. When its density and temperature derivatives are consistently retained, the resulting equation of state reproduces high-accuracy reference data with excellent fidelity. The results demonstrate that the success of first-order perturbation theory is governed primarily by the physical content of the reference system and by the consistent treatment of its state dependence, rather than by the formal truncation order of the expansion.
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All authors A. Trokhymchuk, V. Hordiichuk, R. Melnyk, I. Nezbeda
Mesoscale and Nanoscale Physics
3D integration of a hybrid quantum dot circuit-QED device for fast gate dispersive charge readout and coherent spin-photon coupling
Sebastien Granel, Frederic Gustavo, Jean-Luc Thomassin et al. (+8 more)
Hybrid
circuit quantum electrodynamics (cQED) aims at coupling various
quantum degrees of freedom, among which are
spin and charge degrees of freedom in gate defined
quantum dots,
phonons or
magnons... with quantized electromagnetic fields in superconducting microwave cavities to investigate fundamental physics questions or for
quantum computation and simulation. However, low microwave losses, key for many hybrid cQED experiments, are challenging to achieve given the often exotic and/or complex material stacks (e.g. semiconducting material, ferromagnets, or piezoelectric materials) required to host the various
quantum degrees of freedom. In this work, we present a 3D-integration process to overcome this challenge for semi-industrial silicon MOS
spin qubits. The process is based on dense indium bump interconnects at a pitch of 10 $\mathrm{\mu}$m and superconducting thin films of Niobium Nitride (NbN). First, we report on DC and RF interconnect properties that demonstrate a high galvanic interconnection yield and internal quality factors above $10^{5}$ in the single
photon regime for NbN resonators interrupted by a single indium bump interconnect. Eventually, we fabricated a 3D-integrated hybrid
circuit quantum electrodynamics (cQED) device based on a semi-industrial MOS hole double
quantum dot and a high impedance NbN resonator. For this device, we report a cavity internal quality factor above 10000 and demonstrate record sensitivity for gate-based dispersive readout of the charge degree of freedom with an SNR of 100 in 300 ns. Finally, we demonstrate strong
spin-
photon coupling of $g_{s}/2\pi$ = 75 MHz, which highlights the viability of 3D-integration for
quantum dot based hybrid
spin circuit quantum electrodynamics and opens to high-fidelity
spin readout and microwave
photon-based remote
spin qubit entanglement.
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All authors Sebastien Granel, Frederic Gustavo, Jean-Luc Thomassin, Heimanu Niebojewski, Benoit Bertrand, Frederic Berger, Alain Gueugnot, Chafik Mhamdi, Etienne Dumur, Romain Maurand, Simon Zihlmann
Materials Science
Global DIC-based sample-detector geometry refinement for accurate EBSD indexing
Claire Griesbach and Dennis M. Kochmann
Electron backscatter diffraction is a powerful tool for mapping crystallographic microstructures. However, the primary crux to improving orientation accuracy and applying the technique to challenging materials lies in the correct calibration of the sample-detector geometry. Many approaches have aimed at overcoming this barrier through various pattern center calibration strategies, but the pattern center only defines part of the sample-detector geometry. Here, we present a DIC-based geometry refinement method that obtains a single map-consistent sample-detector geometry, refining both the pattern center and sample/detector angles. We effectively decouple the local orientation changes from the global geometry effects on the Kikuchi patterns by calculating the consistent map-wide simulated-to-experimental pattern shifts associated with global geometry parameter errors. Using single-
crystal silicon and barium titanate (a material possessing six pseudosymmetric variants) as model materials, we demonstrate improved map-wide orientation consistency and more robust discrimination of pseudosymmetric variants than the Nelder-Mead and Differential
Evolution optimization strategies.
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Superconductivity
Bragg-Williams order competes with superconductivity
Xu Liu, Xu Chen, Chuizhen Chen et al. (+14 more)
Orderings in charge and
spin have been extensively studied to unravel their correlation to emergent superconductivity over the past decades. Bragg-Williams order (BWO), a classical structural order parameter describing site occupancy in
alloys, has long been speculated to influence superconducting behavior. Yet, its role still remains ambiguous, largely due to the difficulty of isolating BWO from concomitant charge doping or competing electronic instabilities. Here, we establish In2/3PSe3 as a platform wherein indium vacancies are reversibly configurable between ordered and disordered states via thermal treatment. We show that the disordered phase undergoes a pressure-induced superconducting transition with a Tc of 11 K, significantly higher than the 7 K observed in its ordered counterpart. This constitutes a rare instance in which pure BWO variation drives a substantial shift in Tc. By combining a Ginzburg-Landau phenomenological analysis with a BCS-McMillan microscopic description, we demonstrate that BWO naturally suppresses superconductivity through electron-
phonon interactions, a mechanism supported by ultra-low-wavenumber Raman measurements. Our findings support BWO as an independent order parameter that competes directly with superconductivity, extending the concept of competing orders beyond conventional electronic and
magnetic degrees of freedom.
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All authors Xu Liu, Xu Chen, Chuizhen Chen, Boqin Song, Jing Chen, Xijing Dai, Qinghua Zhang, Feng Jin, Xingya Wang, Weiwei Dong, Dongliang Yang, Gefei Li, Pengju Zhang, Jiangping Hu, Jian-gang Guo, Tianping Ying, Xiaolong Chen
Statistical Mechanics
Restoration of Ensemble Equivalence by Quantum Fluctuations
Alessandro Campa and Andrea Trombettoni
We study the thermodynamic phase diagram of a one-dimensional
quantum spin chain subjected to both mean-field and nearest-neighbor interactions, and to a transverse
magnetic field $h$. The purpose is to determine the effect of the
quantum fluctuations, due to the transverse field, on the phase diagram, in particular with respect to the occurrence of ensemble inequivalence. We denote our model as a
quantum Nagle-Kardar model. To perform the calculation of the canonical partition function, we show that, due to the presence of the mean-field term, in the thermodynamic limit one can use the Hubbard-Stratonovich transformation in spite of the non-commutativity of the different operators appearing in the
Hamiltonian, and we adopt a procedure of successive approximations that lead to the determination of the phase diagram thanks to a scaling property of the phase transition lines. The results show that the ensemble inequivalence, present in the classical Nagle-Kardar model, is removed above a threshold value $h_c$ for the transverse field. For $h$ larger than $h_c$ the phase diagram exhibits only second-order phase transition lines, implying therefore restoration of ensemble equivalence.
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Soft Condensed Matter
Universal material basis for biocompatible printed electrolytes in Organic Electrochemical Transistors
Moritz Flemming, Paul Zechel, Rakesh R. Nair et al. (+7 more)
Organic Electrochemical Transistors (OECTs) stand out for their interplay between ionic and electronic conduction, making them ideal analogues to biological synapses for neuromorphic computing and biosensing applications. Furthermore, they can be printed into integrated
circuits on flexible substrates, enabling low-cost and high-throughput fabrication of complete electronic systems. However, most OECT electrolytes for integrated
circuits still lack biocompatibility and suffer from rheology-related printing challenges. This paper presents a novel material basis that can be combined with an ionic
liquid to fabricate an electrolyte for OECTs that only contains biocompatible materials. It allows rheological adjustments to enable the use of electrolyte in both inkjet and screen printing. Furthermore, the electrolyte is UV-curable, enabling it to transition into solid-state structures after printing. Extended ink and device lifetimes for screen-printed structures enable the fabrication of advanced OECTs that can operate in ambient air for over 30 days after fabrication. Ultimately, a fully screen-printed transistor using only biocompatible materials on a leaf substrate is shown
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All authors Moritz Flemming, Paul Zechel, Rakesh R. Nair, Emil Mahnke, Markus Löffler, Alyna Ong, Bernd Rellinghaus, Lukas M. Eng, Karl Leo, Hans Kleemann
Superconductivity
Geometric Rashba Control of Polar Pairing at a-LaAlO$_3$/KTaO$_3$ Interfaces
Yi Zhou
At amorphous-LaAlO$_3$/KTaO$_3$ interfaces, superconductivity coexists with switchable polar nanoregions (PNRs), and $T_c$ depends quasi-linearly on crystallographic orientation. We propose a minimal theoretical framework in which overdamped PNR fluctuations mediate pairing, while
geometric Rashba coupling controls its angular dependence. Within a reduced isotropic helicity-band description, the leading dynamic Rashba vertex scales as $\sin\theta$, where $\theta$ is the angle between the interface normal and the $[100]$ axis, yielding $\lambda(\theta)=\lambda_0+C\sin^2\theta$. Numerical Matsubara–Eliashberg solutions show that this nonlinear mapping reproduces the observed quasi-linear $T_c(\theta)$. Because the Rashba-activated polar channel is amplified by the large atomic
spin-orbit coupling of Ta $5d$ orbitals, the framework also offers a parametric—not yet quantitative—rationale for why KTaO$_3$ interfaces are both more orientation-sensitive and higher-$T_c$ than their SrTiO$_3$ counterparts.
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Statistical Mechanics
Finite-time transitions in optimal control and non-equilibrium relaxation
Jan Meibohm, Samuel Monter, Sarah A. M. Loos et al. (+1 more)
We theoretically and experimentally study finite-time optimal control of a colloidal particle steered through a spatially inhomogeneous environment, modeled by a position-dependent energetic cost at the final state. The competition between this state-dependent penalty and path-dependent dissipation gives rise to a sharp transition in the control strategy at a critical control duration. We further show that this transition can be linked to a dynamical phase transition in nonequilibrium relaxation after a quench, where the control cost maps onto the rate function governing rare trajectories.
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All authors Jan Meibohm, Samuel Monter, Sarah A. M. Loos, Clemens Bechinger
Strongly Correlated Electrons
Pareto Frontier of Neural Quantum States: Scalable, Affordable, and Accurate Convolutional Backflow for Strongly Correlated Lattice Fermions
Yuntian Gu, Zeyao Han, Wenrui Li et al. (+5 more)
Neural
Quantum States (NQS) are now among the most accurate methods for studying strongly correlated many-
fermion systems, outperforming existing many-body approaches for large systems. However, NQS calculations remain extremely resource-intensive. Here, we introduce a new Pareto frontier of efficiency and accuracy for NQS in simulating strongly correlated
lattice fermions, defined by two complementary backflow-related architectures: the Sparse Convolutional Ansatz for
Lattice Electrons (SCALE) (state-of-the-art efficiency) and the Accurate Convolutional ansatz for
lattice Electrons (ACE) (state-of-the-art accuracy), benchmarked on the iconic Hubbard and $t-J$ models for large
lattices. SCALE uses a tailored convolutional design enabling efficient local updates via low-rank determinant updates, reducing computational scaling from $O(N^4)$ to $O(N^3)$ in backflow methods and yielding a >40$\times$ practical speed-up in tests while maintaining high variational accuracy. As an application, we study the previously inaccessible 1/8-doped pure Hubbard model up to $32 \times 32$, finding no significant energy difference between horizontal and vertical filled stripe states - contrasting with half-filled stripe states when next-nearest-neighbor hoppings are included. ACE employs a deep convolutional stack to maximize expressive power, achieving unprecedented accuracy on large systems. Extensive
benchmarks on Hubbard and $t-J$ models show SCALE delivers variational energies competitive with leading methods at a fraction of the cost, while ACE sets a new accuracy
benchmark, surpassing recent results with only 1/6 the runtime for $16 \times 4$ systems. These new NQS approaches provide scalable, affordable, and accurate tools for exploring strongly correlated fermionic physics, such as the microscopic mechanism of unconventional superconductivity.
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All authors Yuntian Gu, Zeyao Han, Wenrui Li, Zhiyu Xiao, Tao Xiang, Mingpu Qin, Liwei Wang, Dingshun Lv
Mesoscale and Nanoscale Physics
Linear response from tilted Dirac cones under strain-induced pseudomagnetic fields
Sanskar Sharma and Ipsita Mandal
We investigate the transport signatures of pseudo-Landau levels (PLLs) in two-dimensional anisotropic Dirac systems with tilted cones, whose effective bandstructure results from strain-induced pseudogauge fields. In contrast to conventional Landau quantisation, the PLLs exhibit explicit momentum-dependence by being dispersive, leading to finite longitudinal group-velocities. We analyse the transport properties within the semiclassical Boltzmann framework by computing the electrical, thermoelectric, and thermal response in the linear regime, which acquire nonzero longitudinal components. We also check the validity of the Mott relation and Wiedemann-Franz law in our system. Our results provide a unified framework for understanding the interplay between tilted spectrum and structural deformation in affecting
quantum transport, and suggest unambiguous experimental signatures in strain-engineered systems.
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Materials Science
Predicting challenging phase transitions with Bayesian active learning
Lorenzo Bastonero, Gabriel Joalland, Chiara Cignarella et al. (+2 more)
Materials underpin modern technologies, from energy harvesting, storage, and conversion to information and communication technologies. Their functionality is often governed by the interplay between competing phases, as thermodynamic behavior shapes microscopic properties and ultimately determines technological performance; for instance, the light absorption of inorganic metal-halide perovskites in
solar cells. Accurately predicting
crystal thermodynamics, however, remains a major challenge for computational approaches because strong anharmonic effects require extensive sampling of the potential energy surface. Here, we present an on-the-fly
Bayesian framework, combined with the
stochastic self-consistent harmonic approximation, for learning first-principles interatomic potentials. This approach enables the prediction of thermodynamic properties over a broad temperature range with first-principles accuracy while requiring training on only a few tens to a few hundreds of atomic configurations. To demonstrate its power, we investigate the thermodynamic and dynamical properties of Li$_2$O, $\alpha$-CsPbI$_3$, and $\delta$-CsPbI$_3$, requiring only 44, 256, and 50 total-energy calculations, respectively. Notably, we show that this framework accurately captures the phase diagram of CsPbI$_3$, which explains its spontaneous degradation into the non-absorbing yellow phase, predicting the transition temperature with remarkable accuracy and efficiency. More broadly, the method presented opens a novel route toward accelerated materials engineering under realistic conditions for a wide range of technologically relevant applications, including solid-state batteries, optoelectronic devices, and memristors.
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All authors Lorenzo Bastonero, Gabriel Joalland, Chiara Cignarella, Lorenzo Monacelli, Nicola Marzari